Handle authentication errors (closes #98)

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Disable offline mode before upgrading to XMPP (fixes #174)

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Show presence status in a different style while updating (closes #145)

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>